Display devices comprising liquid crystalline compounds (the term "liquid crystalline compounds" is used in this specification as a general term for the compounds which exhibit a liquid crystal phase and for the compounds which do not exhibit a liquid crystal phase but are useful as a component of liquid crystal compositions) have widely been utilized for the display of watches, tabletop calculators, word processors, or the likes. In connection with the display devices, researches on in-plane switching (IPS) mode and vertical alignment (VA) mode by which characteristics of viewing angle can be improved at a low manufacturing cost are extensively conducted in recent years.
In liquid crystal compositions for the IPS mode or VA mode, those having a negative dielectric anisotropy value are preferable, and such physical properties as a high voltage holding ratio, low threshold voltage, their small temperature dependency, wide temperature range of liquid crystal phase, excellent miscibility with other liquid crystal materials, and low viscosity are sought for the compositions.
As a component of such liquid crystal compositions, many liquid crystalline compounds in which fluorine atom substituted at their lateral position were investigated and, for example, the following compounds are disclosed in the literatures. ##STR2##
However, they have such problems that the compounds of 1) are high in threshold voltage and that the compounds of 2) and 3) are low in transition temperature to isotropic phase or tend to exhibit smectic phase, and thus the compounds of 2) and 3) hardly from a stable nematic phase particularly at low temperatures when used as component of liquid crystal compositions.